Ni-Fe alloys having high magnetic permeability are widely used as materials for magnetic cores such as cores of transformers for communication instruments, small motors, clocks, watches and the like. For such core materials, excellent magnetic permeability and high saturated magnetic flux density are required as direct current magnetic characteristics. For example, materials for clock cores and yokes should have a magnetic permeability (.mu..sub.m) of not less than 35,000 and a saturated magnetic flux density (B.sub.10) of not less than 11,000 G.
Conventionally, 45%-Ni Permalloy (trademark), which has the most excellent magnetic permeability and saturated magnetic flux density among the Ni-Fe magnetic alloys, is used as magnetic core materials to satisfy the above-mentioned requirements. Recently, however, it is desirable to make compact magnetic cores for various devices and the requirements for high performance magnetic cores are getting more and more severe. Under the circumstances, magnetic materials having improved magnetic permeability and saturated magnetic flux density are needed.
Japanese Laid-Open Patent Publication No. 142749/87 describes an attempt to improve the magnetic properties of magnetic materials by reducing O and S contents. Japanese Laid-Open Patent Publication No. 227065/87 describes another attempt wherein Mo is added and P and S contents are limited.
Alloys of 80%-Ni Permalloy series (JIS-PC corresponding to ASTM A753) exhibit the highest magnetic permeability and have the maximum magnetic permeability (.mu..sub.m) of not less than 100,000, which is much higher than that achieved by alloys of JIS-PB series. However, the saturated magnetic flux density B.sub.10 of the former is not satisfactory being at the level about 7000 G. Furthermore, JIS-PC alloys are expensive because they contain no less than about 80% of expensive Ni and the application thereof is limited due to this economical factor.
Accordingly, the object of the present invention is to provide an inexpensive soft magnetic alloy containing a reduced amount of Ni which is provided with the maximum magnetic flux density B.sub.10 of not less than 11,000 and the maximum magnetic permeability (.mu..sub.m) comparable to that of JIS-PC.
The inventors conducted extensive studies in search for a Ni-Fe soft magnetic alloy so as to achieve the above-mentioned object and found that a Ni-Fe-Cr soft magnetic alloy comprising 40-52% of Ni, 0.5-5% of Cr, not more than 0.003% of S, not more than 0.005% of O, not more than 0.005% of B and balance iron has a high saturated magnetic flux density B.sub.10 and a high maximum magnetic permeability (.mu..sub.m) of not less than 100,000.